It is desirable to be able to track containers or other objects, for example during shipment of a container. One known technique for tracking a container is to mount a radio frequency identification (RFID) tag on the container. The RFID tag can transmit wireless signals, and typically can also receive wireless signals.
In more detail, there are RFID tags capable of receiving wireless signals transmitted by a signpost, where these wireless signals contain a digital code that uniquely identifies a particular signpost. These tags then transmit tag signals that contain a unique code identifying the tag as well as the unique code identifying the signpost. In circumstances where the transmission ranges or fields of two signposts effectively overlap, a tag moving through the overlap region is likely to receive signpost signals from each of the two tags in an alternating manner. It can be problematic if the tag repeatedly “flip-flops” back and forth between recognizing one signpost and recognizing the other signpost. A suitable technique to avoid this is desirable.
A different consideration is that, in order to successively load or unload a plurality of containers to or from a location such as the cargo hold of a ship, a large crane is typically used. It would be advantageous to have a technique for tracking containers while they are being moved by such a crane.